fix warning in html form class (#31860) #117

Job	Run time
pre-commit / pre-commit	3m 4s
phan / Run phan	3m 12s
phpstan / php-stan (8.2)	1m 22s
gh-travis	0s
windows-ci / win-test (windows-latest, 7.4)	7m 56s
	15m 34s

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